Heading out on a Sunday morning to mow the lawn is nice, especially when the mower only takes one or two pulls to start. However, mowing loses all its fun when the mower acts up and dies right after starting. So, if you’re one of the unlucky ones with a lawn mower that starts and then dies right away, you will have to head back to the shed and grab some tools to get the mower fixed.
Why is My Mower Starting Then Dying? (The Short Answer)
A lawn mower that starts but won’t stay running could face several mechanical problems. Here are four common causes that may be the source of the problem.
- Dirty Carburetor
- Clogged Fuel System
- Bad Fuel
- Defective/Dirty Spark Plug
Check These 7 Things If Your Lawn Mower Starts Then Dies
So before you ditch the lawn mower for a new one or pay for an expensive repair, let’s take a look at what you can do. Here are seven things to check that could be the root causes of your lawn mower troubles.
Blocked Carburetor Jet & Fuel Float
The carburetor is one of the first places I look whenever my push mower starts and then dies. If the carburetor jet or float becomes clogged or jammed, the engine quickly becomes fuel starved. This is why the engine will stall straight after it has fired up. So, grab yourself a small socket wrench and remove the bolt holding the carburetor’s fuel cup to the carburetor.
Once you remove the cup, you’ll be able to see if the fuel float can move freely or if it’s jammed. If it doesn’t move freely, then you’ll know why the fuel is being starved and causing the engine to stall.
Next, you’ll need to inspect the jet. In some cases, the bolt you removed that holds the fuel cup on is actually the jet. This is common for engines such as Briggs & Straton. You’ll usually find the jet centered between the fuel float for other carburetors. If you have a screwdriver at hand, you should easily be able to unscrew the fuel jet.
With either type of jet, once you have it removed, you’ll have to look to see if it is blocked or not. I like to hold it up to the light to see if I can see through the tiny jet hole. If you can’t, you’ll have found why your lawn mower won’t stay running.
Clogged-Up Fuel System
Clogged fuel systems are more common than you would think. The fuel systems can quickly become clogged if you have a dusty and sandy yard. Also, if you allow debris, like grass clippings, to get into the fuel tank, you’ll find your fuel system gets clogged quicker than it should.
So, if the lawn mower runs and dies, you’ll want to check the following fuel system parts.
- Fuel Filter
- Fuel Pump
- Fuel Line
Checking the Fuel Filter
The fuel filter is the first thing I like to test in the fuel system. A lot of the time, these are see-through parts that can be inspected in a few seconds. If you have a transparent fuel filter, then inspect it to see if it looks discolored or has debris inside.
You’ll have to remove those that are not transparent and give the inflow side a tap on a hard surface, like a workbench. If you find that debris or dirt comes out of the filter, then you’ll more than likely have to change out the filter.
Checking the Fuel Pump
The quickest way to test the pump is to disconnect the fuel line from the carburetor. The fuel line is the line between the fuel pump and the carburetor. Then, place the detached line into a small container, like a cup, and give the engine a pull.
Once you pull the starter cord, the engine activates the fuel pump. If everything works as it should, then fuel should steadily flow from the detached fuel line. If it doesn’t, then you have diagnosed an issue between the fuel tank and the pump.
Checking for Clogged Fuel Lines
Clogged fuel lines are usually caused by debris getting into the tank and then into the fuel line. One defense you have is the fuel filter, which doesn’t stop blockages in the fuel line before the filter.
So, if you disconnect the fuel filter from the fuel line going to the fuel tank, fuel should flow freely out of the line. If it doesn’t, you could have found the cause of the issue. Replacing the affected fuel line on your mower could be the solution.
Checking if Your Fuel is Bad
Bad fuel is a lot less combustible than fresh fuel. If you manage to get an engine running with bad fuel, it’s either going to cut out pretty quickly or run poorly. Usually, it’s going to cut out quickly. What about other symptoms of bad gas in a lawn mower? A quick visual inspection is what I like to do to definitely tell if this is the issue.
Grab yourself two small clear containers and a plastic syringe. Use the syringe to suck out some fuel from the lawn mower’s fuel tank and place it into one of the cups. Then place some fresh fuel into the second cup. If the fuel from the lawn mower’s tank is a darker color, more yellow or brown, then it means the gas has gone bad, and you need to get it removed.
Problem with the Spark Plug
An intermittent spark is a common symptom of a bad or dirty spark plug. This means that the spark can’t be produced accurately to ignite the vaporized fuel in the cylinder head. The engine will stall if the spark isn’t produced at the right time and with the right sized spark.
Using an inline plug tester is the quickest, safest, and most accurate way to check a lawn mower spark plug. This small inline device tells you if the plug is working correctly. I don’t really recommend just looking at the end of the spark plug for a spark, as this doesn’t give you a complete picture. So, if you don’t already have a tester, I’d recommend grabbing yourself one.
How to Fix a Mower that Won’t Stay Running (My Favorite Tips and Tricks)
If you’ve found why your lawn mower starts and then dies from my list of causes, then you next need to know how to fix the problem. Let’s take a closer look at how to repair each item on the list and what tools you’ll need to get the job done.
Unblocking a Carburetor Jet
Inspecting a carburetor jet requires you to complete half of the work of getting it clean. Removing the jet is half of the job. Once you have the jet in hand, you can either try to clean it or simply replace the part.
To clean it, all you need to do is remove the blockage and then clean it. I find all you need to use is a wire small enough to pass through the hole in the jet. Poke the wire through the hole in the jet and push out any blockage.
Also, blockages are not always bits of debris. Jets can get blocked by fuel that has gummed up and reduce the size of the hole. So, grab some carburetor cleaner and give the jet a good spray. Once the cleaner has worked its way into the dirt, use the wire to reopen the jet’s hole.
After you finish, you can put the carburetor back together and try the engine.
Tools Needed to Unblock a Carburetor Jet
- Thin Wire
- Carburetor Cleaning Spray
Unblocking a Fuel Float
Again, inspecting the float is half the job. Once it is exposed, lift the float up and down a few times and free it up. A tiny piece of grit is enough to create a problem with the fuel float, and lifting it up and down can be enough to fix it.
If you find that the float is stiff and won’t move, then spraying it with a carburetor cleaner should be enough to free up the movement. Once it moves freely, the carburetor can be put back together and tested.
Tools Needed to Unblock a Fuel Float
- Carburetor Cleaner
Changing the Fuel Filter
The most important thing about changing a fuel filter is using the correct replacement. Fuel filters are specific to the engine and the fuel flow rate. If you use the wrong one, you will probably end up with the same problem you started with—the lawn mower starts and then dies because of the incorrect fuel flow.
So, take a set of needle nose pliers and remove the clips holding the fuel line in place on the fuel filter. Then, remove the fuel lines from both ends of the filter.
Next, attach the fuel line to your new fuel filter and reposition the spring clips using your pliers. When you’re installing the new filter, be sure to install it the correct way. An arrow on the side should indicate the direction of the fuel flow.
Tools & Parts Needed to Change a Fuel Filter
- Replacement Fuel Filter
- Needle Nose Pliers
Replacing the Fuel Pump
If you have discovered that your fuel pump is acting up and won’t pump as it should, then you’ll need to replace it. Check all the other items on the fuel system first to make sure it’s not something else causing the pump to have a problem.
When you are confident that the pump is at fault, you’ll have to remove it and install a new one. So, start by switching off the fuel and grab your pliers. Once the fuel is off, take your needle nose pliers and remove the spring clips holding the fuel line to the pump. On ride-on lawn mowers, you’ll find three lines.
- Fuel Line Between Pump & Carburetor
- Fuel Line Between Pump & Fuel Filter
- Line Between Pump & Overhead Valve
So, when the spring clips are removed, you’ll have to then remove the 3 lines. Next, remove the bolts holding the fuel pump onto the engine. Usually, on the bigger lawn mowers, you’ll find two bolts. A small socket wrench should do the trick to remove the bolts.
Once these bolts are removed, the pump will be detached from the engine. Now it’s time to install the new pump. All you do is reverse the process. Position the pump on the engine, install the bolts, install the line, and reclip the lines.
Once all this is completed, you can give the engine a try. It’s going to take a minute to start the engine as the fuel system will not have any gasoline in it. Just remember to switch the gas back on.
Tools & Parts Needed to Change a Fuel Pump
- New Fuel Pump
- Needle Nose Pliers
- Small Socket Wrench Set
Unclogging the Fuel Lines
If you find that a fuel line is blocked, you’ll need to figure out how and why. A fuel line that is blocked by old fuel gumming the line will more than likely need to be replaced. But if your lines are blocked with debris, then a pipe cleaner should be enough to get fuel flowing again.
So, take a pair of pliers and remove the spring clips holding the pipe in place. Once the clips are out of the way, the line should come loose.
Next, poke a pipe cleaner through the fuel line. Anything that was stuck in the line should be dislodged fairly easily. Once you have the pipe cleared, it can then be reinstalled on the lawn mower with the clips repositioned.
Tools & Parts Needed to Unblock a Fuel Line
- Pipe Cleaner
- Pliers
Removing the Bad Fuel
If you have performed a fuel test and found that the gasoline in the mower is bad, then you’ll need a way to remove it from the mower. But don’t worry – fixing a bad gas problem with a lawn mower is usually straightforward.
Some small mowers can be tipped over, and the gasoline poured out. With two people, this is a pretty easy job. If you have a bigger lawn mower that is too heavy to tip, then you’re going to have to use a siphon or a pump to drain the gas from your mower.
To siphon or pump out the gasoline from your lawn mower, place the inflow end of the siphon/pump into the lawn mower’s gas tank and the outflow end into a spare gas can.
To transfer the fuel, you just need to turn on the pump or start the siphoning process. Once the gasoline has been completely drained, you can fill the tank with fresh gasoline and strike up the lawn mower. It’s going to take a few pulls to flush out the old gas and get the new gas through the fuel system, so expect several pulls to get the engine started up.
The 2 main things to remember are that the pump/siphon needs to be suitable for gasoline transfer and that you need to dispose of the bad gas safely.
Tools & Parts Needed to Drain/Siphon Bad Fuel
- Siphon/Pump
- Spare Fuel Tank
Changing out the Spark Plug
The spark plug is last on my list of potential reasons your lawn mower starts and then dies. You’ll first need to get a new spark plug and a plug wrench to change the spark plug. It only takes a few minutes to change out a spark plug once you have all the necessary materials.
First, remove the ignition cable from the end of the spark plug and tuck it out of the way. Then, take your plug wrench and remove the spark plug. Next, place the new spark plug into the engine and tighten it in place using your fingers.
Once the plug is finger-tight, switch to your spark plug wrench and finish tightening. Just be careful not to tighten the plug too much. Once the plug is installed, replace the ignition cable and give the engine a test.
Tools & Parts Needed to Change a Sparkplug
- New Spark Plug
- Plug Wrench
If None of These Fixes Help…
There comes a time that repairs are beyond what we can achieve in our garages and sheds. Some of the issues can require replacement parts, such as a new carburetor, which for a lot of people, is too big of a job to take on. Before you book any work at a repair shop, I suggest you research the costs. Parts and labor for repairs can mount up and sometimes get close to what it costs to replace the lawn mower with a new one.
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